DMM Working Group A. Yegin
Internet-Draft Actility
Intended status: Standards Track D. Moses
Expires: December 16, 2016 Intel
K. Kweon
J. Lee
J. Park
Samsung
June 14, 2016
On Demand Mobility Managementdraft-ietf-dmm-ondemand-mobility-04
Abstract
Applications differ with respect to whether they need IP session
continuity and/or IP address reachability. The network providing the
same type of service to any mobile host and any application running
on the host yields inefficiencies. This document describes a
solution for taking the application needs into account in selectively
providing IP session continuity and IP address reachability on a per-
socket basis.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 16, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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connections. IP address reachability is essential for mobile hosts
to use specific/published IP addresses.
Mobile IP is designed to provide both IP session continuity and IP
address reachability to mobile hosts. Architectures utilizing these
protocols (e.g., 3GPP, 3GPP2, WIMAX) ensure that any mobile host
attached to the compliant networks can enjoy these benefits. Any
application running on these mobile hosts is subjected to the same
treatment with respect to the IP session continuity and IP address
reachability.
It should be noted that in reality not every application may need
those benefits. IP address reachability is required for applications
running as servers (e.g., a web server running on the mobile host).
But, a typical client application (e.g., web browser) does not
necessarily require IP address reachability. Similarly, IP session
continuity is not required for all types of applications either.
Applications performing brief communication (e.g., DNS client) can
survive without having IP session continuity support.
Achieving IP session continuity and IP address reachability by using
Mobile IP incurs some cost. Mobile IP protocol forces the mobile
host's IP traffic to traverse a centrally-located router (Home Agent,
HA), which incurs additional transmission latency and use of
additional network resources, adds to the network CAPEX and OPEX, and
decreases the reliability of the network due to the introduction of a
single point of failure [I-D.ietf-dmm-requirements]. Therefore, IP
session continuity and IP address reachability should be be provided
only when needed.
Furthermore, when an application needs session continuity, it may be
able to satisfy that need by using a solution above the IP layer,
such as MPTCP [RFC6824], SIP mobility [RFC3261], or an application-
layer mobility solution. Those higher-layer solutions are not
subject to the same issues that arise with the use of Mobile IP since
they can utilize the most direct data path between the end-points.
But, if Mobile IP is being applied to the mobile host, those higher-
layer protocols are rendered useless because their operation is
inhibited by the Mobile IP. Since Mobile IP ensures the IP address
of the mobile host remains fixed (despite the location and movement
of the mobile host), the higher-layer protocols never detect the IP-
layer change and never engage in mobility management.
This document proposes a solution for the applications running on the
mobile host to indicate whether they need IP session continuity or IP
address reachability. The network protocol stack on the mobile host,
in conjunction with the network infrastructure, would provide the
required type of IP service. It is for the benefit of both the users
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and the network operators not to engage an extra level of service
unless it is absolutely necessary. So it is expected that
applications and networks compliant with this specification would
utilize this solution to use network resources more efficiently.
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Solution3.1. Types of IP Addresses
Three types of IP addresses are defined with respect to the mobility
management.
- Fixed IP Address
A Fixed IP address is an address assigned to the mobile host by the
network with a guarantee to be valid for a very long time, regardless
of whether it is being used in any packets to/from the mobile host,
or whether or not the mobile host is connected to the network, or
whether it moves from one point-of-attachment to another (with a
different subnet or IP prefix) while it is connected.
Fixed IP address are required by applications that need both IP
session continuity and IP address reachability.
- Session-lasting IP Address
A session-lasting IP address is an address assigned to the mobile
host by the network with a guarantee to be valid through-out the IP
session(s) for which it was requested. It is guaranteed to be valid
even after the mobile host had moved from one point-of-attachment to
another (with a different subnet or IP prefix).
Session-lasting IP addresses are required by applications that need
IP session continuity but do not need IP address reachability.
- Non-persistent IP Address
This type of IP address provides neither IP session continuity nor IP
address reachability. The IP address is obtained from the serving IP
gateway and it is not maintained across gateway changes. In other
words, the IP address may be released and replaced by a new IP
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address when the IP gateway changes due to the movement of the mobile
host.
Applications running as servers at a published IP address require a
Fixed IP Address. Long-standing applications (e.g., an SSH session)
may also require this type of address. Enterprise applications that
connect to an enterprise network via virtual LAN require a Fixed IP
Address.
Applications with short-lived transient IP sessions can use Session-
lasting IP Addresses. For example: Web browsers.
Applications with very short IP sessions, such as DNS client and
instant messengers, can utilize Non-persistent IP Addresses. Even
though they could very well use a Fixed of Session-lasting IP
Addresses, the transmission latency would be minimized when a Non-
persistent IP Address is used.
3.2. Granularity of Selection
The IP address type selection is made on a per-socket granularity.
Different parts of the same application may have different needs.
For example, control-plane of an application may require a Fixed IP
Address in order to stay reachable, whereas data-plane of the same
application may be satisfied with a Session-lasting IP Address.
3.3. On Demand Nature
At any point in time, a mobile host may have a combination of IP
addresses configured. Zero or more Non-persistent, zero or more
Session-lasting, and zero or more Fixed IP addresses may be
configured on the IP stack of the host. The combination may be as a
result of the host policy, application demand, or a mix of the two.
When an application requires a specific type of IP address and such
address is not already configured on the host, the IP stack shall
attempt to configure one. For example, a host may not always have a
Session-lasting IP address available. In case an application
requests one, the IP stack shall make an attempt to configure one by
issuing a request to the network. If the operation fails, the IP
stack shall fail the associated socket request. If successful, a
Session-lasting IP Address gets configured on the mobile host. If
another socket requests a Session-lasting IP address at a later time,
the same IP address may be served to that socket as well. When the
last socket using the requested IP address is closed, the IP address
may be released or kept for future applications that may be launched
and require a Session-lasting IP address.
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In some cases it might be preferable for the mobile host to request a
new Session-lasting IP address for a new opening of an IP session
(even though one was already assigned to the mobile host by the
network and might be in use in a different, already active IP
session). It is out of the scope of this specification to define
criteria for selecting to use available addresses or choose to
request new ones. It supports both alternatives (and any
combination).
It is outside of the scope of this specification to define how the
host requests a specific type of address (Fixed, Session-lasting or
Non-persistent) and how the network indicates the type of address in
its advertisement of addresses (or in its reply to an address
request).
The following are matters of policy, which may be dictated by the
host itself, the network operator, or the system architecture
standard:
- The initial set of IP addresses configured on the host at the boot
time.
- Permission to grant various types of IP addresses to a requesting
application.
- Determination of a default address type when an application does
not make any explicit indication, whether it already supports the
required API or it is just a legacy application.
3.4. Conveying the Selection
The selection of the address type is conveyed from the applications
to the IP stack in a way to influence the source address selection
algorithm [RFC6724].
The current source address selection algorithm operates on the
available set of IP addresses when selecting an address. According
to the proposed solution, if the requested type IP address is not
available at the time of the request, the IP stack shall make an
attempt to configure one such IP address. The selected IP address
shall be compliant with the requested IP address type, whether it is
selected among available addresses or dynamically configured. In the
absence of a matching type (because it is not available and not
configurable on demand), the source address selection algorithm shall
return an empty set.
A Socket API-based interface for enabling applications to influence
the source address selection algorithm is described in [RFC5014].
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That specification defines IPV6_ADDR_PREFERENCES option at the
IPPROTO_IPV6 level. That option can be used with setsockopt() and
getsockopt() calls to set and get address selection preferences.
Furthermore, that RFC also specifies two flags that relate to IP
mobility management: IPV6_PREFER_SRC_HOME and IPV6_PREFER_SRC_COA.
These flags are used for influencing the source address selection to
prefer either a Home Address or a Care-of Address.
Unfortunately, these flags do not satisfy the aforementioned needs
due to the following reasons, therefore new flags are proposed in
this document:
- Current flags indicate a "preference" whereas there is a need for
indicating "requirement". Source address selection algorithm does
not have to produce an IP address compliant with the "preference" ,
but it has to produce an IP address compliant with the "requirement".
- Current flags influence the selection made among available IP
addresses. The new flags force the IP stack to configure a compliant
IP address if none is available at the time of the request.
- The Home vs. Care-of Address distinction is not sufficient to
capture the three different types of IP addresses described in
Section 2.1.
The following new flags are defined in this document and they shall
be used with Socket API in compliance with the [RFC5014]:
IPV6_REQUIRE_FIXED_IP /* Require a Fixed IP address as source */
IPV6_REQUIRE_SESSION_LASTING_IP /* Require a Session-lasting IP
address as source */
IPV6_REQUIRE_NON-PERSISTENT_IP /* Require a Non-persistent IP address
as source */
Only one of these flags may be set on the same socket. If an
application attempts to set more than one flag, the most recent
setting will be the one in effect.
When any of these new flags is used, then the IPV6_PREFER_SRC_HOME
and IPV6_PREFER_SRC_COA flags, if used, shall be ignored.
These new flags are used with setsockopt()/getsockopt(),
getaddrinfo(), and inet6_is_srcaddr() functions [RFC5014]. Similar
with the setsockopt()/getsockopt() calls, getaddrinfo() call shall
also trigger configuration of the required type IP address, if one is
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not already available. When the new flags are used with
getaddrinfo() and the triggered configuration fails, the
getaddrinfo() call shall ignore that failure (i.e., not return an
error code to indicate that failure). Only the setsockopt() shall
return an error when configuration of the requested type IP address
fails.
The following new error codes are also defined in the document and
will be used in the Socket API in compliance with [RFC5014].
EAI_REQUIREDIPNOTSUPPORTED /* The network does not support the
ability to request that specific IP address type */
EAI_REQUIREDIPFAILED /* The network could not assign that specific IP
address type */
4. Backwards Compatibility Considerations
Backwards compatibility support is required by the following 3 types
of entities:
- The Applications on the mobile host
- The IP stack in the mobile host
- The network infrastructure
4.1. Applications
Legacy applications that do not support the new flags will use the
legacy API to the IP stack and will not enjoy On-Demand Mobility
feature.
Applications using the new flags must be aware that they may be
executed in environments that do not support On-Demand Mobility
feature. Such environments may include legacy IP stack in the mobile
host, legacy network infrastructure, or both. In either case, the
API will return an error code and the invoking applications must
respond with using legacy calls without On-Demand Mobility feature.
4.2. IP Stack in the Mobile Host
New IP stacks must continue to support all legacy operations. If an
application does not use On-Demand Mobility feature, the IP stack
must respond in a legacy manner.
If the network infrastructure supports On-Demand Mobility feature,
the IP stack may still request specific types of source IP address
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transparently to legacy applications. This may be useful for
environments in which both legacy and new applications are executed.
The definition of what type of addresses to request and how they are
assigned to legacy applications are outside of the scope of this
specification.
4.3. Network Infrastructure
The network infrastructure may or may not support the On-Demand
Mobility feature. How the IP stack on the host and the network
infrastructure behave in case of a compatibility issue is outside the
scope of this API specification.
5. Summary of New Definitions
The following list summarizes the new constants definitions discussed
in this memo:
<netdb.h> IPV6_REQUIRE_FIXED_IP
<netdb.h> IPV6_REQUIRE_SESSION_LASTING_IP
<netdb.h> IPV6_REQUIRE_NON_PERSISTENT_IP
<netdb.h> EAI_REQUIREDIPNOTSUPPORTED
<netdb.h> EAI_REQUIREDIPFAILED
<netinet/in.h> IPV6_REQUIRE_FIXED_IP
<netinet/in.h> IPV6_REQUIRE_SESSION_LASTING_IP
<netinet/in.h> IPV6_REQUIRE_NON_PERSISTENT_IP
<netinet/in.h> EAI_REQUIREDIPNOTSUPPORTED
<netinet/in.h> EAI_REQUIREDIPFAILED
6. Security Considerations
The setting of certain IP address type on a given socket may be
restricted to privileged applications. For example, a Fixed IP
Address may be provided as a premium service and only certain
applications may be allowed to use them. Setting and enforcement of
such privileges are outside the scope of this document.
7. Acknowledgements
We would like to thank Alexandru Petrescu, John Kaippallimalil, Jouni
Korhonen, Seil Jeon, and Sri Gundavelli for their valuable comments
and suggestions on this work.
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